1. Sample Volume
For 5 mm outer diameter NMR tubes, we recommend a “three-fingers” high sample volume as optimal, equivalent to approximately 0.6 ml.
2. Sample Concentration
The relevant concentrations in NMR are the number of moles of a nucleus with a unique chemical shift. A good guess for a first time run is in the range of mM or a few mg’s. The more concentrated the sample, the better the signal-to-noise. If there is aggregation at high concentrations, the line widths will be broad and J-couplings may not be resolvable (easily fixed by dilution of the NMR sample).
To increase the signal-to-noise ratio by a factor of two, you either need twice as much sample or 22 the time.
Any sample that has not dissolved (is not in solution) will not give a high-resolution NMR signal and will probably degrade the quality of the spectrum obtained. If you have particulate material, filter the sample.
3. Sample Handling
Start with clean tubes (new tubes are not clean, rinse them first with deuterated solvent). Prepare your samples in your own lab. Wipe the outside of the tube clean, before arriving to the NMR facility. Leave your gloves and lab coat behind. Before placing your NMR tube (with the spinner) into the magnet, once again wipe the outside of the tube and also the spinner.
Recommended reading:
A.E. Derome, Modern NMR Techniques for Chemistry Research, Pergamon Press, Oxford, 1987, pp. 36-37.
Rider University, NMR Collaborative Training Project